[PATCH 2/6] mm: page_alloc: Document why NR_ALLOC_BATCH is always updated

[Mel Gorman]

From: Johannes Weiner <hannes@xxxxxxxxxxx>

Needs-signed-off
---
 mm/page_alloc.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index f861d02..61e9e8c 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1547,7 +1547,15 @@ again:
 					  get_pageblock_migratetype(page));
 	}
 
+	/*
+	 * All allocations eat into the round-robin batch, even
+	 * allocations that are not subject to round-robin placement
+	 * themselves.  This makes sure that allocations that ARE
+	 * subject to round-robin placement compensate for the
+	 * allocations that aren't, to have equal placement overall.
+	 */
 	__mod_zone_page_state(zone, NR_ALLOC_BATCH, -(1 << order));
+
 	__count_zone_vm_events(PGALLOC, zone, 1 << order);
 	zone_statistics(preferred_zone, zone, gfp_flags);
 	local_irq_restore(flags);
-- 
1.8.4

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